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Statistics 202: Statistical Aspects of Data Mining Professor David Mease

Statistics 202: Statistical Aspects of Data Mining Professor David Mease Tuesday, Thursday 9:00-10:15 AM Terman 156 Lecture 2 = Start chapter 2 Agenda: 1) Assign Chapters 1 and 2 Homework due 7/10 2) Lecture over first part of chapter 2. Homework Assignment:

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Statistics 202: Statistical Aspects of Data Mining Professor David Mease

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  1. Statistics 202: Statistical Aspects of Data Mining Professor David Mease Tuesday,Thursday 9:00-10:15AM Terman 156 Lecture 2 = Start chapter 2 Agenda: 1) Assign Chapters 1 and 2 Homework due 7/10 2) Lecture over first part of chapter 2

  2. Homework Assignment: Chapters 1 and 2 homework is due Tuesday 7/10 Either email to me (dmease@stanford.edu), bring it to class, or put it under my office door. SCPD students may use email or use courier. The assignment is posted at http://www.stats202.com/homework.html

  3. Introduction to Data Mining by Tan, Steinbach, Kumar Chapter 2: Data

  4. What is Data? • An attribute is a property or characteristic of an object • Examples: eye color of a person, temperature, etc. • Attribute is also known as variable, field, characteristic, or feature • A collection of attributes describe an object • Object is also known as record, point, case, sample, entity, instance, or observation Attributes Objects

  5. Reading Data into Excel Download it from the web at www.stats202.com/stats202log.txt The right click on it and select “Open With” then “Choose Program”

  6. Reading Data into Excel Choose Excel Oops! Everything is in the first column! Solution: click on the first column then select “Data” then “Text to Columns”

  7. Reading Data into Excel Choose “Delimited” and hit “Next”

  8. Reading Data into Excel Check only “Space” then “Next” again

  9. Reading Data into Excel Q: Why did this work? Why don’t all spaces cause column splits?

  10. Reading Data into Excel Q: Why did this work? Why don’t all spaces cause column splits? A: The file is escaped using quotes. (read http://en.wikipedia.org/wiki/Delimiter for more information)

  11. Reading Data into R Download it from the web at www.stats202.com/stats202log.txt Set your working directory: > setwd("C:/Documents and Settings/Administrator/Desktop") Read it in: > data<-read.csv("stats202log.txt", sep=" ",header=F)

  12. Reading Data into R Look at the first 5 rows: > data[1:5,] V1 V2 V3 V4 V5 V6 V7 V8 V9 1 69.224.117.122 - - [19/Jun/2007:00:31:46 -0400] GET / HTTP/1.1 200 2867 www.davemease.com 2 69.224.117.122 - - [19/Jun/2007:00:31:46 -0400] GET /mease.jpg HTTP/1.1 200 4583 www.davemease.com 3 69.224.117.122 - - [19/Jun/2007:00:31:46 -0400] GET /favicon.ico HTTP/1.1 404 2295 www.davemease.com 4 128.12.159.164 - - [19/Jun/2007:02:50:41 -0400] GET / HTTP/1.1 200 2867 www.davemease.com 5 128.12.159.164 - - [19/Jun/2007:02:50:42 -0400] GET /mease.jpg HTTP/1.1 200 4583 www.davemease.com V10 V11 V12 1 http://search.msn.com/results.aspx?q=mease&first=21&FORM=PERE2 Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322) - 2 http://www.davemease.com/ Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322) - 3 - Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322) - 4 - Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4 - 5 http://www.davemease.com/ Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4 -

  13. Reading Data into R Look at the first column: > data[,1] [1] 69.224.117.122 69.224.117.122 69.224.117.122 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 … … … [1901] 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 [1911] 65.57.245.11 67.164.82.184 67.164.82.184 67.164.82.184 171.66.214.36 171.66.214.36 171.66.214.36 65.57.245.11 65.57.245.11 65.57.245.11 [1921] 65.57.245.11 65.57.245.11 73 Levels: 128.12.159.131 128.12.159.164 132.79.14.16 171.64.102.169 171.64.102.98 171.66.214.36 196.209.251.3 202.160.180.150 202.160.180.57 ... 89.100.163.185

  14. Experimental Vs. Observational Data • (Important but not in book) • Experimental data describes data which was collected by someone who exercised strict control over all attributes. • Observational data describes data which was collected with no such controls. Most all data used in data mining is observational data so be careful. • Examples: -Diet Coke vs. Weight -Carbon Dioxide in Atmosphere vs. Earth’s Temperature

  15. Types of Attributes: • Qualitative vs. Quantitative (P. 26) • Qualitative (or Categorical) attributes represent distinct categories rather than numbers. Mathematical operations such as addition and subtraction do not make sense. Examples: eye color, letter grade, IP address, zip code • Quantitative (or Numeric) are numbers and can be treated as such. Examples: weight, failures per hour, number of TVs, temperature

  16. Types of Attributes (P. 25): • All Qualitative (or Categorical) attributes are either Nominalor Ordinal. • Nominal = categories with no order • Ordinal = categories with a meaningful order • AllQuantitative (or Numeric) attributes are either Interval or Ratio. • Interval = no “true” zero, division makes no sense • Ratio = true zero exists, division makes sense

  17. Types of Attributes: • Some examples: • Nominal • Examples: ID numbers, eye color, zip codes • Ordinal • Examples: rankings (e.g., taste of potato chips on a scale from 1-10), grades, height in {tall, medium, short} • Interval • Examples: calendar dates, temperatures in Celsius or Fahrenheit, GRE score • Ratio • Examples: temperature in Kelvin, length, time, counts

  18. Properties of Attribute Values • The type of an attribute depends on which of the following properties it possesses: • Distinctness: =  • Order: < > • Addition: + - • Multiplication: * / • Nominal attribute: distinctness • Ordinal attribute: distinctness & order • Interval attribute: distinctness, order & addition • Ratio attribute: all 4 properties

  19. Discrete vs. Continuous (P. 28) • Discrete Attribute • Has only a finite or countably infinite set of values • Examples: zip codes, counts, or the set of words in a collection of documents • Often represented as integer variables • Note: binary attributes are a special case of discrete attributes which have only 2 values • Continuous Attribute • Has real numbers as attribute values • Can compute as accurately as instruments allow • Examples: temperature, height, or weight • Practically, real values can only be measured and represented using a finite number of digits • Continuous attributes are typically represented as floating-point variables

  20. Discrete vs. Continuous (P. 28) • Qualitative (categorical) attributes are always discrete • Quantitative (numeric) attributes can be either discrete or continuous

  21. In class exercise #3: Classify the following attributes as binary, discrete, or continuous. Also classify them as qualitative (nominal or ordinal) or quantitative (interval or ratio). Some cases may have more than one interpretation, so briefly indicate your reasoning if you think there may be some ambiguity. a) Number of telephones in your house b) Size of French Fries (Medium or Large or X-Large) c) Ownership of a cell phone d) Number of local phone calls you made in a month e) Length of longest phone call f) Length of your foot g) Price of your textbook h) Zip code i) Temperature in degrees Fahrenheit j) Temperature in degrees Celsius k) Temperature in kelvins

  22. Types of Data in R • R often distinguishes between qualitative (categorical) attributes and quantitative (numeric) • In R, qualitative (categorical) =“factor” quantitative (numeric) =“numeric”

  23. Types of Data in R • For example, the IP address in the first column of stats202log.txt is a factor • > data[,1] • [1] 69.224.117.122 69.224.117.122 69.224.117.122 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 128.12.159.164 • … • … • [1901] 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 65.57.245.11 • [1911] 65.57.245.11 67.164.82.184 67.164.82.184 67.164.82.184 171.66.214.36 171.66.214.36 171.66.214.36 65.57.245.11 65.57.245.11 65.57.245.11 • [1921] 65.57.245.11 65.57.245.11 • 73 Levels: 128.12.159.131 128.12.159.164 132.79.14.16 171.64.102.169 171.64.102.98 171.66.214.36 196.209.251.3 202.160.180.150 202.160.180.57 ... 89.100.163.185 • > is.factor(data[,1]) • [1] TRUE > data[,1]+10 [1] NA NA NA NA NA NA NA NA… Warning message: + not meaningful for factors …

  24. Types of Data in R • However, the 8th column looks like it should be numeric. Why is it not? How do we fix this? • > data[,8] • [1] 2867 4583 2295 2867 4583 2295 1379 2294 4432 7134 2296 2297 3219968 1379 2294 4432 7134 2293 2297 2294 … • [1901] 2294 4432 7134 2294 4432 7134 2294 2867 4583 2295 2294 4432 7134 2294 4432 7134 2294 2294 2294 2294 • [1921] 2294 2294 • Levels: - 1135151 122880 1379 1510 2290 2293 2294 2295 2296 2297 2309 238 241 246 248 250 2725487 280535 2867 3072 3219968 4432 4583 626 7134 7482 • > is.factor(data[,8]) • [1] TRUE • > is.numeric(data[,8]) • [1] FALSE

  25. Types of Data in R • A: We should have told R that “-” means missing when we read it in. • > data<-read.csv("stats202log.txt", • sep=" ",header=F, na.strings = "-") • > is.factor(data[,8]) • [1] FALSE • > is.numeric(data[,8]) • [1] TRUE

  26. Types of Data in Excel • Excel is not quite as picky and allows you to mix types more • Also, you can change between a lot of different predefined formats in Excel by right clicking a column and then selecting “Format Cells”

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